The host star has a different makeup than our own Sun, being relatively lacking in metallic elements -- a discovery that demonstrates that habitable planets can form in a greater variety of environments than previously believed.

Publishing their findings in the Astrophysical Journal Letters, and also available at http://arxiv.org/archive/astro-ph, the team said the planet has a mass at least 4.5 times that of Earth and orbits its host star about once every 28 days, meaning its year equals about one Earth month.

Data was analyzed from the European Southern Observatory on the GJ 667C star, which is an M-class dwarf star that puts out much less heat than our Sun. The team believes there are at least three planets orbiting close to the star, with one being close enough that it could support life, with similar temperatures that we have on Earth.

“This was expected to be a rather unlikely star to host planets. Yet there they are, around a very nearby, metal-poor example of the most common type of star in our galaxy,” said UC Santa Cruz astronomer Steven Voght. “The detection of this planet, this nearby and this soon, implies that our galaxy must be teeming with billions of potentially habitable rocky planets.”

GJ 667C had previously been observed to have a super-Earth-like planet (GJ 667Cb), but the findings were never published. The planet, however, orbits too close to the star and would not be a suitable planet to host liquid water. The team were collecting data on this planet when they found the clear signal of the new planet (GJ 667Cc). The team said it receives about 90 percent of the light that Earth receives; however, because most of its incoming light is in the infrared, more of this incoming energy should be absorbed by the planet, giving it about the same amount as the Earth absorbs from the sun.

But the theory about water will not be confirmed until astronomers learn more about the planet´s atmosphere.

Some experts have been skeptical that M-class dwarf stars could have planets in the habitable zone because they are too dim and tend to have lots of solar flare activity that can emit lethal doses of radiation to nearby planets.

But the new findings could indicate those experts are wrong. Astronomers are intrigued by the possibilities that these stars could in fact host planets within the habitable zone, suitable for both life and water.

At least two other planets had been discovered within the past year that may also potentially be within the habitable zone. In May, French astronomers confirmed the first exoplanet, Gliese 581d, about 20 light years away, to meet the key requirements to support life. And Swiss astronomers in August discovered planet HD 85512b, about 36 light years away, that seemed to also be within the habitable zone.